Load dependent control circuit for a gasoline fuel injection unit

ABSTRACT

A monostable multivibrator produces fuel injection pulses, the length of which are made dependent on the engine rpm by a control voltage fed to a first voltage divider at the input of the multivibrator. Whenever the pulse exceeds a predetermined length, corresponding to full-load operation of the engine, a time delay circuit connects the second voltage divider in parallel with the first voltage divider so as to diminish the effect of the rpm dependent correction on the pulse length.

United States Patent Eisele et al.

[ 51 July 24, 1973 LOAD DEPENDENT CONTROL CIRCUIT FOR A GASOLINE FUELINJECTION UNIT Inventors: Hermann Eisele, Ditzingen;

Wolfgang Reichardt, Stuttgart, both of Germany Robert Bosch GmbH,Stuttgart, Germany Filed: Mar. 22, 1971 Appl. No.: 126,649

Assignee:

Foreign Application Priority Data Mar. 28, 1970Germany................... P 20 15 183.1

US. Cl. 123/32 EA, 1231140 MC, 123/32 R Int. Cl. F021) 3/00 Field ofSearch 123/32 CH, 140 MC References Cited UNITED STATES PATENTS 11/1971Weasel 123/32 BA 7/1970 Schmidt 123/32 3,430,616 3/1969 016C116: 123/1193,515,104 6/1970 1161611311, 123/32 3,543,734 12/1970 Mair 123/323,483,851 12/1969 126161131161 123/32 OTHER PUBLICATIONS AircraftCarburetion Thorner 1947 Pages 38-41, 82-85.

Primary Examiner-Laurence M. Goodridge Assistant Examiner-Ronald B. CoxAtt0rney-Michael S. Striker 57 ABSTRACT A monostable multivibratorproduces fuel injection pulses, the length of which are made dependenton the engine rpm by a control voltage fed to a first voltage divider atthe input of the multivibrator. Whenever the pulse exceeds apredetermined length, corresponding to full-load operation of theengine, a time delay circuit connects the second voltage divider inparallel with the first voltage divider so as to diminish the effect ofthe rpm dependent correction on the pulse length.

13 Claims, 8 Drawing Figures Patented July 24, 1973 3,747,575

2 Sheets-Sheet 1 lNVENTORS Hermann EKSELE WolfgongRElCHARDT theirATTORNEY LOAD EEPENDENT CONTROL CIRCUIT FOR A GASOLINE FUEL INIECTIONUNIT BACKGROUND OF THE INVENTION The invention relates to a controlcircuit for operating at least one electromagnetic fuel injection sprayvalve of an internal combustion engine. The circuit includes amonostable multivibrator having an input transistor and an outputtransistor, the rectangular pulse output of the multivibratordetermining the open time of the fuel injection valve. The controlvoltate at the base of the input transistor varies the pulse length independence on the engine rpm. The control voltage periodically varies intime with the pulses and is fed to a voltage divider at the input of themultivibrator.

With injection units of this kind, the amount of fuel for each stroke ismetered by the open period of the respective fuel injection valves,which latter receives fuel at a practically constant pressure. Thelength of the fuel injection pulse is controlled by the feedback circuitof the multivibrator, which advantageously has an iron core inductor,the inductance of which is changed in dependence on the pressure in theintake manifold behind the throttle valve. Rpm-dependent correction isobtained (the feedback remaining unchanged)'by producing a controlvoltage that lengthens or shortens the period of the unstable state ofthe multivibrator. The control voltage is generated at the end of aninjection pulse by a regulating circuit having two or more switchingtransistors. V

In a control circuit of the kind described in the first paragraph ofthis section, an. automatic, rpmdependent, control voltage is fed to thetap of the voltage divider. The control voltage controls the length ofthe injection pulse. A transformer, acting as a timing component, hasone end of its secondary winding connected to this tap and the other endto the base of the input transistor of the'multivibrator.

With this known circuit, the rpm-dependent corrections are equallyeffective for all loadings of the internal combustion engine. Forvarious designs of internal combustion engines, it is, nevertheless,desirable and frequently necessary to alter, independence on load, thosecorrectionsusually obtained atloads of 60-80 percent of maximum load andgiving a minimum of exhaust.

SUMMARY OF THE INVENTION An object of theinvention is an internalcombustion engine that enables modification of the rpm-dependentcorrections so as to take into account the load on the engine.

Briefly, the control circuit of the invention consists of triggercircuit means for producing electric injection pulses for opening thefuel injection valve, regulating circuit means, connected to the triggercircuit means, for delivering a control voltage that periodically variesin time with the pulses for varying the length of the pulses independence on engine speed, and time delay circuit means, connected tothe trigger circuit means,

for so negating the effect of the control voltage when the engine isworking at full load that the open time of the fuel injection valve issuited to the full-load operation of the engine.

The novel features which are considered as characteristic for theinvention are set forth in particular in the appended claims. Theinvention itself, however,

both as to its construction and its method of operation, together withadditional objects and advantages thereof, will be best understood fromthe following description of specific embodiments when read inconnection with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a circuit diagram showing anembodiment of the invention;

FIG. 2 is a graph showing the variation in the length of the injectionpulses in dependence on engine speed;

FIGS. 3a through 3e plot voltage against time at several importantpoints in the circuit shown in FIG. I; and

FIG. 4 is a circuit diagram showing a modification of part of thecircuit shown in FIG. I.

DESCRIPTION OF THE PREFERRED EMBODIMENTS With reference to FIG. I, thefuel injection unit is intended for a four cylinder internal combustionengine I of which the spark plugs 2 are connected to a high voltageignition system, not shown. The electromagnetic fuel injectionspra'yvalves 4 are mounted, immediately adjacent the inlet valves (not shown),on the branches of the intake manifold 3 leading to the respectivecylinders. Each valve 4i is connected by a respective fuel line 5 to adistributor 6. A pump 7, driven by an electric motor (not shown), keepsthe fuel in the distributor 6'and the fuel lines 5 at an approximatelyconstant pressure of about 2 atmospheres.

Each of the fuel injection spray valves 4 comprises a solenoid (notshown), one end of which is connected to ground and the other end ofwhich is connected by a respective lead d to one of the four resistors9. These resistors are connected in pairs to the collector of a respective one of the two power transistors It) and II, which are part ofan electronic control circuit that will be described.

In addition to the power transistors 10 andll, the control circuitincludes a monostalble multivibrator l2 (enclosed within the dashed-linebox). The multivibrator comprises an input transistor T1, an outputtransistor T2, and an iron core inductor 13, the latter serving as atiming component. i

The iron core inductor III is constructed as a transformer and hasamovable core part 14, which is connected to an adjusting rod I5 that,in turn, is connected to the diaphragm (not shown) of a pressure box 16.The suction side of the pressure box is connected to the intake manifold3 just behind the engine throttle valve 18, which is controlled by thefoot pedal 17. When the pressure in the intake manifold falls, thediaphragm of the pressure box I6 raises the movable core part 14 in thedirection of the arrow, thereby enlarging the air gap of the iron core(not shown) of the transformer 13, so that the inductance of the primarywinding 19 of the transformer 13 is smaller the lower the pressure inthe intake manifold 3.

One end of the secondary winding 20 of the transformer 13 is connectedto the base of the input transistor TI and to a resistor R3 connected toa common positive rail 21, whereas the other end of this winding isconnected by the junction H with the tap of a voltage divider composedof two resistors R1 and R2. The resistor R2 is connected to the positiverail 21, and the resistor RI is connected to the common negative railSill, which is connected to ground and to the negative pole of a l2-voltbattery, not shown. The emitters of the transistors T1 and T2 aredirectly connected to the negative rail 30. The collector of the inputtransistor T1 is connected by a resistor R4 to the positive rail 21,whereas the collector of the output transistor T2 is connected to thesame rail by the primary winding 19 of the transformer 13 and a resistorR6 connected in series with this winding. A coupling resistor R connectsthe base of transistor T2 to the collector of transistor T1. Adifferentiating capacitor C1 connects the base of this latter transistorto the stationary contact 23 of a switch of which the movable contact 24is connected to the negative rail 30. The movable contact 24 is operatedby a two-lobed cam 28, which a cam shaft (not shown) connects to thecrank shaft 27 of the engine. Each complete rotation of the crank shaftcloses the switch once and thereby turns off the transistor T1. T0permit charging and discharging of the capacitor C1, the capacitor plateconnected to the switch contact 23 is connected by a resistor 29 to thepositive rail and the other capacitor plate is connected to this samerail by the resistor R3 and to the junction H by the secondary winding20.

Before describing the remaining components of the control circuit, itwill be explained how the varying pressure in the intake manifold 3changes the length of the current pulses J, which determines the openperiod of the fuel injection spray valves 4. A current pulse J isproduced each time that the switch 23,24 is closed.

The transistor T1 is conductive and therefore keeps transistor T2 cutoff during the time immediately preceding the closing of the movablecontact 24. As soon as the cam 28 moves the movable contact 24 againstthe contact 23, the charge held by the capacitor C reduces the voltageat the C1 of transistor T1 to below the potential of the negative rail30, the base becoming negative. The transistor T1 is consequently cutoff, and the multivibrator 12 is triggered to its unstable state inwhich the transistor T2 is conductive. The collector current of thistransistor, flowing to the primary winding 19, increases exponentiallyand causes a strengthening magnetic field in the iron core (not shown)and in the movable core part 14 of the transformer 13. The larger theair gap, and consequently the smaller the inductance of the primarywinding 19, the faster the collector current increases. The increasingcurrent flow induces a feedback voltage in the secondary winding 20. Themaximum value of this feedback voltage occurs at the instant the switch23,24 is closed and is determined by the amount of inductance. Thefeedback voltage falls exponentially and is of such a polarity that ittends to keep the transistor T1 cut off by opposing the positive biasvoltage of the resistor R3, which acts to return the input transistor T1to its stable, conductive state. The transistor T1 returns to this statewhen the feedback voltage induced in the secondary winding 20 is smallerthan the bias voltage.

- The power transistor or 11, connected to transistor T2 by an amplifier32, is held conductive by the transistor T2 as long as the transistor T1is nonconductive. However, as soon as the transistor T1 returns to itsstable, conductive, state, the transistors T2 and 10 or 11 are again cutoff. The pulse J, which opens the valves 4, consequently lasts for aperiod of time that extends from the moment that the switch 23,24 isclosed until the moment at which the transistor T1 is again conductiveand the transistor T2 is cutoff. When the inductance of the primarywinding 19 becomes smaller with falling pressure in the intake manifold3 (thereby permitting the collector current of transistor T2 to increasemore rapidly), the feedback voltage also falls more rapidly; and thetransistor 71 returns sooner to its conductive state. The fuel injectionvalves 4 are therefore closed earlier than when the pressure in themanifold 3 is higher and therefore the inductance of the primary winding19 is greater.

By changing the inductance of the primary winding 19 in the mannerdescribed, it is possible to vary the length of the current pulses J independence on the instantaneous pressure in the manifold 3. Tests indriving and on the stand have shown, however, that the amount of fuel tobe injected must be dependent not only on the pressure in the intakemanifold, but also on the rpm of the engine. Since the lengths of thepulses J are not affected by the engine rpm, the control circuit has afurther unit, which varies the voltage between the negative line 30 andthe junction H in time with the fuel injection. This unit produces avoltage U that varies in accordance with the graph shown in FIG. 3d.

The input transistor T1 returns to its conductive state when the voltagebetween its base and the ground rail 30 is approximately 0.3 volts(germanium) or approximately 0.5 volts (silicon). The length of thepulses J are greater for less positive values of U where U,, is thevoltage measured between the negative rail 30 and the junction betweenthe resistors R1 and R2. The voltage U is superimposed on the controlvoltage U from transistor T6. The voltage at the base of transistor T1is U U,,U U where U is the voltage across the secondary winding 20. Athigher and higher rpms, the

beginnings of the pulses J shift more and more to the left (as seen FIG.3), the length of a pulse J therefore being determined by theinstantaneous value of the voltage U at the end of the pulse. The lengthof the period T,, accordingly lies between the beginning of the controlvoltage U and that moment at which the voltage U determines the lengthof the pulse J. There is consequently a constant relationship betweenthe length T, of a pulse J and the period T,, and therefore the rpm n ofthe engine.

The circuit A in FIG. 1 controls the pulse length T, in dependence onthe engine rpm. As shown in FIG. 2, the length T, should increasesteadily with increasing engine rpm n until the value n,=2,500revolutions per minute, then remains constant until the value n =3,300revolutions per minute, then declines steadily until the value n =4,000revolutions per minute, and then, for higher rpms, remains constant at avalue considerably below the value between n and n,.

The auxiliary regulating circuit A includes a first switching transistorT3, the base of which is connected by a coupling capacitor C2 and aresistor R7 to the junction G of the collector of transistor T1. Thecapacitor C2 provides a constant time delay V1. The emitter of the firstswitching transistor T3, as well as the emitters of two furtherswitching transistors T4 and T5, is directly connected to the negativerail 30; A resistor R8 connects the base of transistor T3 to thepositive rail 21. The base of the second switching transistor T4 isconnected to the positive rail by a resistor R10. The two transistors T3and T4 are normally conductive. A capacitor C3, which also provides aconstant time delay V2, connects the base of transistor T4 to thecollector of transistor T3. A resistor R12 connects the base of thefollowing switching transistor T5 to the collector of transistor T4.Transistor T5 is normally nonconductive, and when conductive it quicklycharges a capacitor C4 through diode D1. The capacitor C4 and itsparallel-connected discharged resistor R15 are shunted across thecollector resistor R14 of the transistor T5. The voltage appearingacross the capacitor C4 during the charging and discharging of thelatter is used to form the control voltage U A transistor T6, connectedemitter-follower, conducts this voltage to the junction H of the voltagedivider R1 and R2. The collector of the transistor T6 is connecteddirectly to the positive rail 21 and the base is connected by a diode D2to the capacitor C4.

The components of circuit A thus far described operate in the followingmanner. As soon as the transistor T1 returns to its conductive state(which is the stable state of the multivibrator) at the end of a pulse J(as at the moment t see FIG. 3), the collector of this transistorabruptly becomes less positive. This sudden change in voltage isconducted by the resistor R7 and the capacitor C2 to the base oftransistor T3, and turns off the latter. The negative voltage appearingat the base of the transistor T3 dies away in accordance with anexponential function across the resistor R8 until, in dependence on thetime delay V1 introduced by the capacitor C2, the transistor T3 is againconductive. Consequently, the collector of this transistor becomesabruptly less positive, this change in voltage being conducted by thecapacitor C3 to the base of the normally conductive switching transistorT4. The transistor T4 cuts off until the capacitor C3 can sufficientlydischarge through the resistor R10 so that the base of transistor T4 ispositive with respect to the emitter. When either transistor T4 or T5 isconductive, the other transistor is nonconductive. When the transistorT5 is conductive at the moment t;, (see FIG. 3), the capacitor C4 cancharge through the diode D1 and the resistor R13 very quickly to avoltage that is determined by the voltage divider R13,R14. When thetransistor T5 cuts off, the capacitor C4 discharges with a long timeconstant beginning at the moment t, through the resistor R15 and thevery high input impedance of the emitter-follower connected transistorT6. The voltage P, across the resistor R15 varies in accordance with thedashed line shown in FIG. 3d. The transistor T6 is conductive at alltimes.

When the internal combustion engine turns over slowly and the period T,of the injection pulses J is consequently long, the capacitor C4 hassufficient time to discharge. Another injection pulse .1, isnotgenerated until the moment t when the switch 23,24 is again closed, theend of the pulse being determined by the absolute value of the. controlvoltage, U at that time. The end of this pulse is denoted in FIG. 3d by1, and the effective value of the control voltage U s is denoted by U Asthe rpm n of the internal combustion engine increases, the period T,,l/n is shorter, and the end of the next injection pulse is shiftedleftward (as'seen in FIG. 3) towards the moment t,: in other words, itis shifted to a more negative value for P The pulse length .T, increaseswith the rpm until n=n, (see FIG.

2); at higher rpms, the end of the next injection pulse occurs duringthe time of the constant value U; U,,, which is conducted by the diodeD3 from the voltate divider R16,R17 to the base of transistor T6.Consequently, the pulse length T, remains constant until n=n assumingthat all other factors remain unchanged.

In order to obtain the desired reduction in the pulse length in therange between n and n;;, a diode D5 con nects a capacitor C5 to thecollector of transistor T4. This capacitor, which is connected to thenegative rail 30, quickly charges between moments t and t and slowlydischarges between moments I, and t through resistor R19. A diode D4ensures that the capacitor C5 influences the transistor T6 only so longas the voltage P at the base of this transistor is more positive thanthe voltage U in other words, with reference to FIG. 3d, P is nearer tothe zero line. When the engine rpm exceeds m the end of the nextinjection pulse occurs before the moment t,; or t the capacitor C5 isstill at nearly full charge, the consequence of which is that the pulselength T, remains virtually constant above n The auxiliary regulatingcircuit A and the thus rpmcorrected (see FIG. 2), intake manifoldpressure dependent, lengths T, of the injection pulses J are given byway of example only. Both the circuit and the resulting rpm-correctionof the pulse lengths can be modified to suit internal combustion enginesof other designs. The curve of FIG. 2 would, in this case, have adifferent shape.

Aside from the question as to the most favorable shape for the curve ofFIG. 2, it is frequently necessary-to obtain, for example, the maximumpower output from the engine-- to suit the amount of fuel injected tothe rpm at full load operation in a way different from the way in whichit is suited to the rpm at less than full load (partial load) operation.In order to permit rpm-corrected fuel injection at full engine load, butwith diminished or strengthened action, there is provided a secondvoltage divider R21,R22, which is connected in parallel with the firstvoltage divider R1,R2, when the engine operates under full load. Thesecond voltage divider is switched in parallel with the first voltagedivider by a transistor T7 of which the emittercollector path, connectedin series with resistor R23, is

connected between the junction It (the tap of the first diode D6 andaresistor R28 to the positive rail 21 and I by a resistor R27 to thenegative rail 30. The predetermined delay time S is provided by acapacitor C6, which is connected to the junction between the diode D6and the resistor R28 and to the junction between a resistor R129,connected to the positive rail 21, and a diode D7 of which the cathodeis connected to a junction K. The voltage at the junction K is at ornear to the and T9 constitutes compensating means in this embodimerit.

During the interval between two fuel injection pulses J, the transistorsT7 and T9 are conductive, and the transistor T8 is non-conductive. Theplate of the capacitor C6 connected to the base of transistor T9 ischarged strongly negative with respect to the other plate of thecapacitor. As soon as the multivibrator 12 is triggered to its unstablestate at the moment t (or t,,) and causes the beginning of a fuelinjection pulse J, the multivibrator output transistor T2 is conductiveand its collector is brought nearly to ground potential, which factcauses the charge on the capacitor C6 to cut off the transistor T9,thereby rendering transistor T8 conductive and the switching transistorT7 also nonconductive. This condition holds true until, at the end ofthe interval S, the capacitor C6 has discharged and permits thetransistor T9 to return to its conductive state at time t (or t When,because the throttle valve 18 is set at partial load, the absolutepressure in the intake manifold 3 is very low and the length T, of theinjection pulse J is consequently short and ends at the moment t (whichoccurs before the moment t at the end of the time delay S), the voltagedivider R21,R22 does not affect the circuit, because the switchingtransistor T7 is stilll non-conductive at time The rpm-dependentcorrection of the control voltage U is fully effective.

On the other hand, when the pressure in the intake manifold is onlyslightly below the outside air pressure, because the throttle valve 18is nearly wide open, the inductor 13 causes a correspondingly longinjection pulse J that ends only after the transistors T9 and T7 havereturned to their original, conductive, states. In this case, thecontrol voltage U has only a diminished effectiveness because of theresistor R18, since both voltage dividers R1,R2, and R21,R22 aresimultaneously effective, and the increased idling current holds thepredetermined direct current voltage at junction II more nearlyconstant.

The length of the comparator pulse S is so chosen that it is longer thanthe interval T, of the injection pulses J (determined by the pressurebox 16 and the transformer 13) throughout the partial load range(throttle valve 18 only partly open). At full-load operation (valve 18completely, or nearly completely, open), the pulse S is shorter than thepulses J. In this way, the lengths of the two pulses J and S areelectrically compared; and it is possible to omit the auxiliary switch(of the kind shown in FIG. 4), which is operated at full load.

In accordance with the invention, it is important that the switchingtransistor T7 changes its state (from conductive to non-conductive, orfrom non-conductive to conductive) each time that a fresh injectionpulse J begins. This is essential for the aforesaid electroniccomparison of the pulses S and J.

The illustrated embodiment enables the curve of FIG. 2 to be influencedby a great number of factors. For example, the ratio between R21 and R22can be chosen to be larger or smaller than that between R] and R2,thereby raising or lowering the voltage at the junction H. The curve canalso be altered by changing the value of resistor R23.

The second embodiment, shown in FIG. 4, is a simplification of thetiming circuit (T7,T8,T9) of FIG. 1 because an electrical switch K1,I(2is mechanically closed when the engine changes from partial load to fullload operation. This switch is connected in the base circuit of an npntransistor T10 of which the collector and collector-resistor R25 (as isthe case with the transistor T8 of the first embodiment) are connectedto the base of the switching transistor T7. In contradistinction to thefirst embodiment, the base of transistor T10 is connected by a resistorR30 to the ground rail 30 and by a diode D8 and two resistors R31 andR32 to the positive rail 21. So long as the switch K1, K2 is opened, asufficiently large base current flows through the diode and the tworesistors to keep the transistor T10 conductive. The switch K1,K2 isoperated in dependence on the position of a gas pedal 17 (as illustratedin FIG. 4) or in dependence on the position of the throttle valve 13.

When the switch K1, K2 is closed, by depressing the accelerator 17, justbefore the valve 18 is completely opened, the transistor T10 is cut off;the transistor T7, however, receives a sufficient base current throughresistor R25 to remain conductive, whereby the voltage divider R21,R22is connected in parallel with the voltage divider R1,R2, with theaforesaid results.

In the embodiment illustrated in FIG. 4, the switch K1,K2 is operated bymeans of its mechanical linkage to the accelerator 17 or to the throttlevalve 18. In accordance with the invention, this switch can be operatedat the change from partial load to full-load-operation in still otherways. There can be utilized, for example, the change in a physicalmagnitude during the change to full-load operation, such as the greatfall in air pressure in the intake manifold 3. To this end, a pressurebox, for example, can be connected to the intake manifold, the diaphragmof the box being subjected on one face to the pressure in the manifold,and on the other face to the outside air pressure. Below a pressuredifference of about 50 to Torr, the switch K1,I(2 can be opened, orclosed.

It will be understood that each of the elements described above, or twoor more together, may also find a useful application in other types ofcircuits differing from the types described above.

While the invention has been illustrated and described as embodied in aload dependent control circuit for a gasoline fuel injection unit, it isnot intended to be limited to the details shown, since variousmodifications and circuit changes may be made without departing in anyway from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can by applying current knowledgereadily adapt it for various applications without omitting featuresthat, from the standpoint of prior art, fairly constitute essentialcharacteristics of the generic or specific aspects of this inventionand, therefore, such adaptations should and are intended to becomprehended within the meaning and range of equivalence of thefollowing claims.

What is claimed as new and desired to be protected by Letters Patent isset forth, in the appended claims.

1. A control circuit for regulating the open period of at least one fuelinjection valve of an internal combustion engine, comprising, incombination trigger circuit means for producing electric valve-openingpulses for opening the fuel injection valve; regulating circuit means,connected to said trigger circuit means, for delivering a controlvoltage that periodically varies in time with said pulses for varyingthe duration of said pulses in dependence on engine speed; and timedelay circuit means, connected to said trigger circuit means, operativewhen said pulses exceed a predetermined pulse-length, for so negatingthe effect of said control voltage when the engine is working at fullload that the open time of said fuel injection valve is suited to fullload operation of the engine.

2. A control circuit for regulating the open period of at least one fuelinjection valve of an internal combustion engine, comprising, incombination, trigger circuit means for producing electric valve-openingpulses for opening the fuel injection valve; regulating circuit meansconnected to said trigger circuit means for varying the pulse-durationof-said valve-opening pulses in dependence upon at least one engineoperating conditionaccording to a first predetermined functionalrelationship; and compensating means, operative only after apredetermined time delay relative to the beginning of each valve-openingpulse, for altering said regulating circuit in such a manner as toeffect a changeover to a second predetermined functional relationshipappropriate for full-load operation of said engine, said compensatingmeans accordingly participating in the determination of thepulse-duration .of valve-opening pulses only when such valve-openingpulses have a duration exceeding said predetermined time delay.

3. In a combustion engine as defined in claim 1, wherein said regulatingcircuit means comprises means for timing the lengths of said pulses as afunction of airflow into the engine.

4. In a combustion engine as defined in claim 1, wherein said regulatingcircuit means comprises means for timing the lengths of said pulses as afunction of airflow into theengine and also as a function of enginespeed.

5. In a combustion engine as defined in claim 4, wherein said controlmeans comprises means operative when said pulses exceed a predeterminedpulse-length to compensate for changes in engine load by changing thefunctional dependence of said pulses on engine speed.

6. In a combustion engine as defined in claim 1, wherein said regulatingcircuit means conprises means for timing the lengths of said pulses as afunction of an engine operating conditiomand wherein said control meanscomprises means operative when said pulses exceed a predeterminedpulse-length to compensate for changes in engine load by changing thefunctional dependence of said pulses on said operating condition.

7. In an engine as defined in claim 8, wherein said monostablemultivibrator includes a first voltage divider, and time delay circuitmeans includes a second voltage divider and switch means for connectingsaid second voltage divider in parallel with said first voltage dividerwhen said pulses exceed said predetermined pulse length.

8. In an engine as defined in claim 1, wherein said trigger circuit is amonostable multivibrator.

9. In an engine as defined in claim 7, wherein said switch means is afirst switching transistor of which the emitter-collector path isconnected between the tap of said first voltage divider and the tap ofsaid second voltage divider.

10. In an engine as defined in claim 9, including a resistor connectedin series with said emitter-collector path.

11. In an engine as defined in claim 10, including means for changingthe conductive state of said first switching transistor at the beginningof each injection pulse and for a predetermined period that is shorterthan the open time of the fuel injection valve at full engine load butlonger than said open time at partial load.

12. In an engine as defined in claim 11, wherein said means is anelectronic switch having at least one transistor and at least one RCnetwork.

13. In an engine as defined in claim 12, further including first andsecond operating voltages, and wherein the emitter of said transistor ofsaid electronic switch is directly connected to said first operatingvoltage, said electronic switch further includinga resistor connectedbetween the base of said transistor and said first operating voltage; aseries-connected resistor and diode connected between said base and saidsecond operating voltage, said diode being connected with such polarityso as to conduct the base current; a resistor connected to said secondoperating voltage; a capacitor connectedbetween said last-named resistorand the junction between said series-connected resistor and diode; and adiode connectedbetween said capacitor at the junction thereof with saidlast-named resistor and a point in the control circuit having a voltageat least approximately equal to that of said second operating voltagebetween successive injection pulses.

is a: as t

1. A control circuit for regulating the open period of at least one fuelinjection valve of an internal combustion engine, comprising, incombination trigger circuit means for producing electric valve-openingpulses for opening the fuel injection valve; regulating circuit means,connected to said trigger circuit means, for delivering a controlvoltage that periodically varies in time with said pulses for varyingthe duration of said pulses in dependence on engine speed; and timedelay circuit means, connected to said trigger circuit means, operativewhen said pulses exceed a predetermined pulse-length, for so negatingthe effect of said control voltage when the engine is working at fullload that the open time of said fuel injection valve is suited to fullload operation of the engine.
 2. A control circuit for regulating theopen period of at least one fuel injection valve of an internalcombustion engine, comprising, in combination, trigger circuit means forproducing electric valve-opening pulses for opening the fuel injectionvalve; regulating circuit means connected to said trigger circuit meansfor varying the pulse-duration of said valve-opening pulses independence upon at least one engine operating condition according to afirst predetermined functional relationship; and compensating means,operative only after a predetermined time delay relative to thebeginning of each valve-opening pulse, for altering said regulatingcircuit in such a manner as to effect a changeover to a secondpredetermined functional relationship appropriate for full-loadoperation of said engine, said compensating means accordinglyparticipating in the determination of the pulse-duration ofvalve-opening pulses only when such valve-opening pulses have a durationexceeding said predetermined time delay.
 3. In a combustion engine asdefined in claim 1, wherein said regulating circuit means comprisesmeans for timing the lengths of said pulses as a function of airflowinto the engine.
 4. In a combustion engine as defined in claim 1,wherein said regulating circuit means comprises means for timing thelengths of said pulses as a function of airflow into the engine and alsoas a function of enGine speed.
 5. In a combustion engine as defined inclaim 4, wherein said control means comprises means operative when saidpulses exceed a predetermined pulse-length to compensate for changes inengine load by changing the functional dependence of said pulses onengine speed.
 6. In a combustion engine as defined in claim 1, whereinsaid regulating circuit means conprises means for timing the lengths ofsaid pulses as a function of an engine operating condition, and whereinsaid control means comprises means operative when said pulses exceed apredetermined pulse-length to compensate for changes in engine load bychanging the functional dependence of said pulses on said operatingcondition.
 7. In an engine as defined in claim 8, wherein saidmonostable multivibrator includes a first voltage divider, and timedelay circuit means includes a second voltage divider and switch meansfor connecting said second voltage divider in parallel with said firstvoltage divider when said pulses exceed said predetermined pulse length.8. In an engine as defined in claim 1, wherein said trigger circuit is amonostable multivibrator.
 9. In an engine as defined in claim 7, whereinsaid switch means is a first switching transistor of which theemitter-collector path is connected between the tap of said firstvoltage divider and the tap of said second voltage divider.
 10. In anengine as defined in claim 9, including a resistor connected in serieswith said emitter-collector path.
 11. In an engine as defined in claim10, including means for changing the conductive state of said firstswitching transistor at the beginning of each injection pulse and for apredetermined period that is shorter than the open time of the fuelinjection valve at full engine load but longer than said open time atpartial load.
 12. In an engine as defined in claim 11, wherein saidmeans is an electronic switch having at least one transistor and atleast one RC network.
 13. In an engine as defined in claim 12, furtherincluding first and second operating voltages, and wherein the emitterof said transistor of said electronic switch is directly connected tosaid first operating voltage, said electronic switch further including aresistor connected between the base of said transistor and said firstoperating voltage; a series-connected resistor and diode connectedbetween said base and said second operating voltage, said diode beingconnected with such polarity so as to conduct the base current; aresistor connected to said second operating voltage; a capacitorconnected between said last-named resistor and the junction between saidseries-connected resistor and diode; and a diode connected between saidcapacitor at the junction thereof with said last-named resistor and apoint in the control circuit having a voltage at least approximatelyequal to that of said second operating voltage between successiveinjection pulses.